1. Field of the Invention
This invention relates to a heart output and circulatory impedance measuring method and apparatus.
2. Description of the Prior Art
It has been known to use radiographic devices to produce radiographic images of the cardiovascular system. See generally U.S. Pat. Nos. 4,204,225; 4,422,146; 4,418,387; and 4,430,749. Various radiographic systems have been designed to show the movement of objects. See U.S. Pat. Nos. 4,204,225; 4,430,749; 4,447,827; and 4,450,478. Subtraction of radiographic images has also been known. See, for example, U.S. Pat. Nos. 4,458,688; 4,398,213; 4,503,459; and 4,399,457.
One of the most widely used methods, sometimes known as ventriculometry, relies on off-line human interaction namely, requiring an operator to carefully outline the ventricular boundary on a cine projection. This is a very time consuming process, and does not yield immediate on-line results which are valuable for studying therapeutic interventions.
The major difficulty in automating ventriculometry is separating the components of ventricular contraction from its displacement during each beat. The heart does not merely contract, but it also moves and rotates at the same time. These additional translation type motions as distinguished from heart contraction, can introduce substantial errors in volume computation, and, may be difficult to handle without human interaction.
Another method for ventricular volume computation, called densitometry, does not delineate the outline of the ventricle, but merely measures the amount of contrast medium contained in the ventricle. This method does not yield very dependable results, mostly due to the fact that the measuring procedure cannot effectively separate the contributions from the medium located in the ventricle and that which has been ejected into the adjacent circulatory system.
In spite of these prior disclosures, there remains a need for a cardiac output and circulatory impedance measuring system and method that efficiently measures these characteristics.